Acetaldehyde is known as a decomposition product of polyesters such as PET. The acetaldehyde imparts an undesirable taste or flavor to bottled water stored in PET bottles. It has been a long sought objective of the industry to reduce the level of acetaldehyde which migrates out of the PET bottle walls into the water or other beverage stored therein. A number of engineering or design changes to extruders, injection molding machines for preforms and bottle making machinery have been made to minimize formation of acetaldehyde when poly(ethylene terephthalate) PET is processed. Modification to the PET composition itself have been made to lower its melting point or its melt viscosity in order to allow less severe thermal or mechanical damage when PET is processed into preforms or bottles.
Aldehydes may be formed in polyamides, for instance polyamide 6 and polyamide 6,6, under conditions of thermal stress. These aldehydes initiate a chain of events that lead to unwanted yellowing and a reduction in mechanical properties.
U.S. Pat. No. 4,361,681 teaches that polyester containing anhydride end-cap agents have a reduced acetaldehyde generation rate.
U.S. Pat. No. 5,459,224 discloses polyesters having 4-oxybenzylidene end-cap agents to impart improved weatherability and photostability, but no mention is made as to evolution of acetaldehyde. However, it is indicated that such polyesters are suitable for food and beverage packaging.
Polyesters can be synthesized by a number of routes known in the art using a variety of catalyst systems. EP 826,713 A1 teaches that lower levels of acetaldehyde occur during copolymerization of PET when a phosphite such as bis(2,4-di-tert-butylphenyl)pentaerythritol phosphite is present during the polymerization.
U.S. Pat. Nos. 4,837,115; 5,258,233; 5,266,413; 5,340,884; 5,648,032 and 5,650,469; and WO 93/20147 A1; WO 93/23474 A1; WO 98/07786 and WO 98/39388 teach the use of polyamides as a means of reducing the concentration of acetaldehyde, presumably via a Schiff-base reaction with the aldehyde, which is reversible in the presence of water.
EP application 191,701A2 describes biaxially oriented containers having excellent barrier properties said container comprising a blend of a poly(ethylene terephthalate) resin and an ethylene-vinyl alcohol copolymer resin. This reference is focused on improved gas barrier properties and is silent as to any reduction of acetaldehyde content.
Japanese Sho 62-257959 describes biaxially stretched vessels built of synthetic resin consisting of poly(ethylene terephthalate) blended with a copolymer of a polyamide, or blended with ethylene-vinyl alcohol at a weight fraction of 0.1 to 15 percent. The examples are limited to a single EVOH polymer (EVEL G110, Kuraray Co.). It is taught that a lower level of acetaldehyde occurs when the EVOH polymer is present.
European application 714,832A1 teaches a method of manufacturing a container comprising poly(ethylene terephthalate), polycarbonate or PEN polyester with an additive in the bottle wall which binds acetaldehyde. The additive is generally described as a polyamide.
U.S. Pat. No. 5,656,221 describes a process of producing polyester with reduced acetaldehyde concentration using certain catalysts or inert gas conditions or by adding an amide compound. These include commercial polyamides or long chain aliphatic amide compounds.
U.S. Pat. No. 5,856,385 teaches the use of polyamide or amide-wax to reduce the level of acetaldehyde which occurs when sorbitol-based clarifying agent is heated in polyolefins.
Copending application Ser. Nos. 09/603,505 and 09/603,506 disclose the use of poly(vinyl alcohol) or an ethylene/vinyl alcohol copolymer and polyhydric alcohols, respectively, towards reducing the residual aldehyde content in PET. Copending application Ser. No. 09/666,679 discloses the use of polyacrylamide, polymethacrylamide or an acrylamide or methacrylamide copolymer with at least one ethylenically unsaturated comonomer towards reducing the residual aldehyde content in PET.
U.S. Pat. No. 4,873,279 discloses a composition comprising a copolyester-carbonate resin, a polyester resin, and a minor amount of a mixture of a polyol and at least one epoxide.
U.S. Pat. No. 4,394,470 discloses a polyethylene terephthalate molding composition with a caramel colorant. The caramel colorant may have been formed in situ from a mono- or disaccharide.
U.S. Pat. No. 5,681,879 discloses a flame-retardant polyester composition comprising a polyester resin, a polyhydric alcohol having not less than 3 hydroxyl groups, an inorganic flame retardant and a halogen-based flame retardant.
WO 00/66659 discloses molding compositions comprising PET and polyhydric alcohol additives for the reduction of acetaldehyde formation.
WO 01/00724 discloses the use of polyols towards reducing acetaldehyde formation in extruded products of PET.
Hydroxylamine derivatives, such as N,N,-dialkylhydroxylamines and N,N-dibenzylhydroxylamine, are well known as useful stabilizers for a variety of polymeric substrates as is taught for example in U.S. Pat. Nos. 4,590,231, 4,668,721, 4,782,105 and 4,876,300, the relevant parts of which are incorporated herein by reference.
U.S. Pat. Nos. 4,649,221, 4,691,015 and 4,703,073 teach the use of polyhydroxylamine compounds, hydroxylamines derived from hindered amines and alkylated N,N-dibenzylhydroxylamine derivatives, respectively, towards stabilizing polyolefins. All three patents teach that the polyolefin compositions are stabilized against degradation and/or discoloration upon exposure to heating at elevated temperatures, to the combustion products of natural gas, to gamma irradiation or to prolonged storage at ambient temperature.
U.S. Pat. Nos. 4,612,393, 4,696,964, 4,720,517 and 4,757,102 disclose the use of various hydroxylamine compounds towards the stabilization of organic materials.
Hydroxylamine stabilizers are also disclosed in U.S. Pat. Nos. 4,831,134, 5,006,577, 5,019,285, 5,064,883, 5,185,448 and 5,235,056.
U.S. Pat. Nos. 4,666,962, 4,666,963, 4,678,826, 4,753,972, 4,757,102, 4,760,179, 4,929,657, 5,057,563, 5,021,479, 5,045,583 and 5,185,448 disclose the use of various substituted hydroxylamine stabilizers towards the stabilization of organic materials.
U.S. Pat. Nos. 5,081,300, 5,162,408, 5,844,029, 5,880,191 and 5,922,794 disclose the use of saturated hydrocarbon amine oxides towards the stabilization of thermoplastic resins.
U.S. Pat. No. 4,898,901 discloses the use of long chain nitrone compounds as process stabilizers for polyolefin compositions.
Despite the efforts towards a solution for reducing aldehydic contaminates in PET water bottles, for example, there still remains a need for more effective solutions.
The instant invention is useful for any polyester or polyamide where aldehydic compounds, for example acetaldehyde, are formed or evolved during thermal processing of said polyester or polyamide. Thermal processing of said polyester or polyamide includes the synthesis thereof, thermal exposure during solid state polymerization (SSP), any injection molding, injection-blow molding or stretch-blow molding used in the manufacture of preforms, parissons, or bottles and containers, or extrusion of film, or during any melt processing of polyester or polyamide above its glass transition temperature and below its decomposition temperature.
The instant invention provides for a lower amount of contaminants (i.e. aldehydes) in PET water bottles thus providing for improved taste or flavor in bottled water or other bottled beverages in said PET containers. The reduction in the amount of acetaldehyde is highly beneficial in this respect.
Further, the compositions of the present invention impart no unacceptable color or haze to PET bottles. “Haze” is an undesirable, perceptible graying effect.